A researcher records the sound (in decibels) during a series of lessons taught by a

substitute teacher at a local elementary school. In his study, he found that the sound was

806 (MSD) decibels. Assuming the data are normally distributed, which of the following is

an appropriate conclusion?

(Sample mean=M=80, and Standard deviation=SD=6)

A) 68% of classes were between 68 and 80 decibels.

B) 5% of classes were louder than 68 decibels.

C) 95% of classes were between 68 and 92 decibels.

D) all of the above